Flux nulled wheel detector

ABSTRACT

An apparatus for detecting the presence of a ferro-magnetic vehicle wheel has been provided. A primary coil energized with an alternating current input signal produces a magnetic field in the vicinity of the rail on which the wheel is moving. A secondary coil responsive to the field is aligned in the primary field such that a null or zero signal exists at the output of the secondary in the absence of a vehicle wheel. The presence of a wheel in the primary field disturbs that field sufficiently to produce an output in the secondary coil, thus providing indication of wheel presence.

United States Patent Bolton [S4] FLUX NULLED WHEEL DETECTOR [72]Inventor: Norman A. Bolton, Scottsville, NY.

[73] Assignee: General Signal Corporation,

Rochester, NY.

[22] Filed: May l8, i970 [2: Appl. No.: 38,085

52 us. ..246/249, 340/258 0 [51] Int. Cl. ..B6ll 13/04 [58] Field ofSearch........246/249; 340/258 C, 258 D [56] References Cited UNITEDSTATES PATENTS 3,210,539 10/1965 Malaquin ..246/249 l0 ll 9 CgiL)OSCILLATOR INDICATI BE$T AVAILABLE coPY, 9 1 9x 72 FOREIGN PATENTS ORAPPLlCATlONS 1/1965 German ....................'246/249 PrimaryExaminer-Arthur L. La Point Assistant Examiner-George H. LibmanAttorney-Harold S. Wynn and Milton E. Kleinman ABSTRACT An apparatus fordetecting the-presence of a ferromagnetic vehicle wheel has beenprovided. A primary coil energized with an alternating current inputsignal produces a magnetic field in the vicinity of the rail on whichthe wheel is moving. A secondary coil responsive to the field is alignedin the primary field such that a null or zero signal exists at theoutput of the secondary in the absence of a vehicle wheel. The presenceof a wheel in the primary field disturbs that field sufficiently toproduce an output in the secondary coil, thus providing indication ofwheel presence.

. Q mwenns -re RECTIFIER OUT PUT LOGIC PAIENTEBnm 10 1912 R m A L H C SO RECTIFIER OUTPUT LOGIC Field Direction Field Direction FIG. 2

FIG. 3

FLUX NULLED WHEEL DETECTOR BACKGROUND OF INVENTION This inventionrelates to presence detection apparatus and in particular tomagnetically responsive vehicle wheel presence detectors.

The apparatus necessary for accurately detecting the presence of avehicle wheel may range from a purely mechanical device such as atreadle switch through electromechanical and purely electronic devicessuch as photoelectric devices and the like. Schemes using magneticallyresponsive devices for detecting the presence of a vehicle wheel havebeen disclosed in the art, but in many cases serious shortcomings arisewhich are difficult to cope with and may require alternate apparatus inorder to achieve the desired result. Some magnetic wheel detectorsutilize inert devices such as a permanent magnet on one side of a wheelpath such as the rail on a railroad right of way and a receiver on theother side which is responsive to the flux associated with the permanentmagnet. A vehicle wheel moving along the railroad right of way uponpassing between the permanent magnet and the receiver diverts the fluxfrom the magnet such that a reaction indicative of wheel presence isgenerated in the receiver. This occurs because the wheels of a railroadvehicle are ferromagnetic and'the presence of the wheel may cause achange in flux patterns which is sensed by the receiver. However, it isthe rate of change in the flux pattern which determines the presence ofa vehicle and if the wheel enters the field of the permanent magnetslowly, a change in the flux pattern may not be sufficient to provideadequate indication of the presence of a wheel. Another alternative tothe magnetic detector again uses a magnet on the inside of a rail and adetector on the same side spaced such that the flange of a vehicle wheelpassing adjacent to the magnet and detection couples the flux to thedetector and when the wheel is not present, there is very little, ifany, coupling of the flux. Under these circumstances, however, a rapidlymoving wheel may not couple the flux from the transmitter for asufficiently long time for an accurate wheel detection. It is thereforeapparent that detectors using magnetically responsive devices aresomewhat limited in their application and in particular may be uselesswhere they are particularly needed. Such needs arise in main lineoperation where the vehicles speeds are rather high and an accurateandrapidly responsive wheel detector is necessary. An example of thisapplication is the use of a wheel detector to establish wheel positionfor a wheel thermal scanner used for hot box detection. An applicationwherein a vehicle speed may be rather slow is the area of railroadclassification yard operations where operating speeds may be in therange of l to 2 miles per hour.

It would be desirable therefore to provide an arrangement which wouldoperate over a complete range of anticipated speeds including thestationary wheel so that designs would not have to be modified for theparticular application.

It is therefore an object of the preset invention to provide anarrangement which substantially obviates the limitations anddisadvantages of the described prior arrangements.

It is another object of the present invention to provide a wheeldetector simplified in its physical arrangement.

It is another object of the present invention to provide an apparatuswhich is inexpensive in its initial construction and subsequentmaintenance requirements.

SUMMARY OF INVENTION An apparatus for detecting the presence of aferromagnetic vehicle wheel along a right of way has been providedincluding a primary coil energized with an alternating current inputsignal for producing a magnetic field in the vicinity of the right ofway. A secondary coil responsive to the field produced by the primary,is aligned in the primary field 'such that a null or zero secondaryoutput exists in the absence of a vehicle wheel. The presence of a wheelin the primary disturbs the field sufficiently to produce in thesecondary, an output providing indication of wheel presence.

For a better understanding of the present invention together with otherand further objects thereof reference is had to the followingdescription taken in connection with the accompanying drawings, whileits scope will b pointed out in the appended claims.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 shows a block diagram of theapparatus necessary forthe practice of the present invention.

FIGS. 2 and 3 show apparatus necessary for an altemate form of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The concept involved in thepresent invention contemplates the use of a nulled device which deliversa zero output when it is undisturbed and provides a substantial outputupon the introduction of that which would tend to disrupt theequilibrium existing in the nulled state.

In its present form, the apparatus of the present invention includesprimary core C and coil 8 energized for producing a magnetic field F byan oscillator 12. Secondary cores 9 and coils C, (L and R) are placed inthe field F such that the flux F passing through the coils c, has noeffect on their output. The coils C, (L and R) may be suitably encasedcoils of wire wrapped around the cores for concentrating the flux,'andhaving output terminals connected to two diodes D and D, in rectifier13. A vehicle moves along the rail 10 on wheel 11. When the wheel 11 isnot in the vicinity of the field F of the primary' coil C the field Foscillates in accordance with the frequency of the oscillator 12, andthe outputs of the secondary coils C, (L and R) remain unresponsivebecause they are positioned in this field so that the flux is nulledthrough their cores 9. It should be noted at this time that only onesecondary C, (L or R) is necessary for vehicle presence detection alone;however, if directional information were desired, two secondaries wouldbe necessary and this condition will be explained further on in thedisclosure. It will be necessary to refer the secondaries C, as C, (L orR) in that discussion but for the present it is sufficient to refer tothem as C,

Although the magnetic field F is shown in FIG. 1 as being elliptical, itis understood that the metal rail [0 partially distorts the magneticvector pattern of the field F between the primary core 8 and thesecondary core 9. When the output signal from the secondary coil adirection normal to the core 9. The presence of the metal vehicle wheel11 in the field F further distorts the magnetic vector pattern of thefield F between primary core 8 and secondary core 9, thereby alteringthe vector pattern of the field F as it crosses the secondary core 9 andthus producing an output signal in secondary coil C,

As the vehicle wheel 11 approaches the position of the detector from theleft, its presence in the field F causes a disruption of thenulledefiect of the secondary coils C,,(L and R). The null effect of the fieldF is disturbed because the intruding wheel 11 has changed the reluctanceof the magnetic circuit of the primary coil C and core 8. This nulledstate was achieved by energizing the primary C and placing the secondarycoil C, and cores 9 in the field until no output is detected at theoutput terminals of the coils C,. It is therefore apparent that once thestate exists, anything which would interfere with the flux pattern Fwould change this delicate state of equilibrium. For convenience, arailroad vehicle wheel is described, however, it is conceivable that theautomobile or other such vehicle might be adaptable to such a system.

As the wheel 1'] approaches secondary coil C, from the left and proceedstowards the other secondary coil C the field F is disturbed. A signal isthence generated in the coils C, (L and R) and their outputs are coupledto rectifier l3.

For simplicity, the rectifier 13 may include two diodes D and D, as thewheel 11 passes through the field F, the signals produced at the outputsof the secondaries C, (L and R) are respectively coupled to each of thediodes and are rectified at opposed polarities. These signals areamplified in the amplifier 14 and transmitted to the output logicapparatus 15. The occurrence of a particular polarity signal first andthen the other polarity, second, is detected by the logic l anddirectional information as well as wheel presence is provided toindications 16.

A brief discussion of the components of this system cooperatingaccording to the principles of the present invention is as follows:Oscillator 12 generates an alternating current signal and couples thesignal to the primary coil C and core- 8. This alternating currentthrough the coil C generates a field F at the coil C and secondary coilsC, and cores 9 are arranged in the field F such that the field has nonet effect on them for producing an output in the coils C,. If a vehiclewheel 1 l approaches the detector apparatus from the left, the field Fis disturbed such that a net signal is produced at the output of C,,,which is coupled to the rectifier l3, amplified at 14 and at logic 15determines the direction of the wheel approach which determination isconfirmed as the wheel passes from C,,, to C, A stopped wheel can bedetected in this situation because any wheel presence in the field F ofcore C disturbs that field, because the system is dynamic. Since thefield F alternates in accordance with the current of oscillator 12, thechanging field F provides its own dynamic signal rather than dependingupon a moving wheel for cutting field lines and generating a current.

In its simpliest form, the system would be operable with merely onesecondary core C, (L or R); however, the additional secondary core plusthe output logic necessary for providing directional indication as wellas presence detection is particularly useful especially in railroadoperations.

FIGS. 2 and 3 showv apparatus which could be used for an alternateembodiment using a Hall'Effect device.

In FIG. 2 the secondary coil C, is wrapped around a split core 17. Theprimary coil C shown in FIG. 1 is no longer driven by oscillator 12 butby some direct cur rent source. A Hall-Effect device 18 is placed inslit 19 in core 17. Again, the coil C, and core 17 is placed in thefield F such that no output is delivered from Hall- Effect device 18.

FIG. 3 illustrates the operation of the Hall-Effect device 18. Inputelectrodes 20 couple a DC. bias across the device, and current flows inthe direction of the dotted arrows. However, if a magnetic field isintroduced across the device 18 (out of drawing), then the current flowsas indicated by the solid arrows in the device to output electrodes 21.The current is detected and amplified by amplifier 22 which provides asignal to output logic l5.

' The operational basis of the embodiment shown in FIGS. 2 and 3 isdynamic, because the current flowing in the I-Iall-Efi'ect device 18 isset by the DC. bias and is flowing as long as said bias exists. Thefield F produced by the primary C has no effect in the device becausethe secondary C, has been placed in the field F such that the net fluxpassing through the core 17 is zero. Once a vehicle wheel disrupts thefield, a net flux passes through secondary core 17 and coil C, causing adeflection in the current flow of the Hall-Effect device 18.

Directional information may be provided as shown in FIG. 1 before, byincluding two secondaries for producing successive presence signals andsubsequent analysis by the output logic. Another alternative is toanalyze the polarity output currents from the I-Iall-Efi'ect device. Anet field (out of the page) as shown in FIG. 2, produces a current Iwith a direction as indicated on the output leads 21. If the net fluxwere reversed (into the page), however, the current would be reversed.It is therefore apparent that directional information may be obtained bypolarity detection of output current.

While there has been described what are at present considered to be thepreferred embodiments of the present invention, it will be obvious tothose skilled in the art that various changes and modifications may bemade therein without departing from the invention and it is thereforeaimed in the appended claims to cover all such changes and modificationsas fall within the spirit and scope of the invention.

What is claimed is:

1. Apparatus for detecting the presence of a ferromagnetic object alonga right of way comprising:

a. a primary core adjacent to the right of way;

b. a primary coil wound on said primary core, said primary coilenergized with an alternating current input signal for generating amagnetic field and said primary coil wound on said primary core beingpositioned relative to the right of way so that a portion of the rightof way is in the magnetic field generated from the primary coil;

c. a secondary core positioned adjacent to and on the same side of theright of way of said primary core and in the magnetic field generatedfrom said primary coil across the portion of the right of way;

d. a secondary coil wound on said secondary core, said secondary coilresponsive to the magnetic field generated from said primary coil;

e. said secondary core aligned in the magnetic field generated from saidprimary coil such that a null or zero output exists across the secondarycoil; and

f. output logic means connected to said secondary coil for detecting thesignal change from the secondary coil as the ferro-magnetic objectproceeding along the right of way interrupts and distorts the magneticfield generated from said primary coil.

2. The apparatus of claim 1 further including another secondary corewith a secondary coil wound thereon and positioned adjacent to theprimary core in the magnetic field generated from the primary coilacross a portion of the right of way and the secondary coil aligned inthe magnetic field such that a null or zero output exists across thesecondary coil; and

said output logic means is connected to both secondary coils and isresponsive to signals from both secondary coils for providingdirectional indication relative to the movement of the ferro-magneticobject past the primary core along'the right of way.

3. The apparatus of claim 2 wherein said secondary coils are arranged toproduce distinctive outputs associated with their position relative tothe primary core as the ferro-magnetic object proceeds along the rightof way and the output logic means is adapted to respond to thedistinctive outputs for providing the directional information.

4. The apparatus of claim 3 wherein an oscillator provides thealternating current input signals and rectifier means coupled to thesecondary coil outputs at opposite polarities provides the distinctiveoutputs for indicating directional information regarding the movement ofthe ferro-magnetic object along the right of way.

5. Apparatus for detecting the presence of a ferromagnetic object alonga right of way comprising:

a. a primary core adjacent to the right of way;

b. a primary coil wound on said primary-core, said primary coilenergized with a direct current input signal for generating a magneticfield and said primary coil wound on said primary core being positionedrelative to the right of way so that a portion of the right of way is inthe magnetic field generated from the primary coil;

0. a secondary core positioned adjacent to said primary core and in themagnetic field generated from said primary coil across a portion of theright of way;

d. a secondary coil wound on said secondary core, said secondary coilresponsive to the magnetic field generated from said primary coil;

. said secondary coil aligned in the magnetic field generated from saidprimary coil such that a null or zero output exists across the secondarycoil;

f. a device biased fro carrying a direct current and located within saidsecondary coil responsive to a net flux therein for producing an outputindicative of the ferro-magnetic object proceeding along the right ofway and through the magnetic field; and

. output logic means connected to said secondary coil for detecting thesignal change from the secondary coil as the ferro-magnetic objectproceeding along the right of way interrupts and distorts the magneticfield generated from said primary coil.

6. The apparatus of claim 5 further including an additional secondarycore with an additional secondary coil wound thereon and alignedadjacent to the primary core similarly as the first secondary core inthe magnetic field generated from the primary coil across a portion ofthe right of way, a second device located within said additionalsecondary coil biased for carrying a direct current responsive to a netflux for providing an object presence signal; and

said output logic means is connected to both secondary coils and isresponsive to signal outputs of both devices for providing directionalindication relative to movement of the ferro-magnetic object past theprimary along the right of way.

7. The apparatus of claim 5 wherein said device is responsive forproducing one polarity signal or another in accordance with thedirection of said net flux.

8. The apparatus of claim 7 wherein said output logic means isresponsive to the signal output of said device for producing directionalindication of the movement of the ferro-magnetic object along the rightof way through the magnetic field in accordance with the polarity ofsaid device output.

9. The apparatus of claim 5 wherein said device comprises a Hall-Effectsolid state semi-conductor.

2. The apparatus of claim 1 further including another secondary corewith a secondary coil wound thereon and positioned adjacent to theprimary core in the magnetic field generated from the primary coilacross a portion of the right of way and the secondary coil aligned inthe magnetic field such that a null or zero output exists across thesecondary coil; and said output logic means is connected to bothsecondary coils and is responsive to signals from both secondary coilsfor providing directional indication relative to the movement of thEferro-magnetic object past the primary core along the right of way. 3.The apparatus of claim 2 wherein said secondary coils are arranged toproduce distinctive outputs associated with their position relative tothe primary core as the ferro-magnetic object proceeds along the rightof way and the output logic means is adapted to respond to thedistinctive outputs for providing the directional information.
 4. Theapparatus of claim 3 wherein an oscillator provides the alternatingcurrent input signals and rectifier means coupled to the secondary coiloutputs at opposite polarities provides the distinctive outputs forindicating directional information regarding the movement of theferro-magnetic object along the right of way.
 5. Apparatus for detectingthe presence of a ferro-magnetic object along a right of way comprising:a. a primary core adjacent to the right of way; b. a primary coil woundon said primary core, said primary coil energized with a direct currentinput signal for generating a magnetic field and said primary coil woundon said primary core being positioned relative to the right of way sothat a portion of the right of way is in the magnetic field generatedfrom the primary coil; c. a secondary core positioned adjacent to saidprimary core and in the magnetic field generated from said primary coilacross a portion of the right of way; d. a secondary coil wound on saidsecondary core, said secondary coil responsive to the magnetic fieldgenerated from said primary coil; e. said secondary coil aligned in themagnetic field generated from said primary coil such that a null or zerooutput exists across the secondary coil; f. a device biased fro carryinga direct current and located within said secondary coil responsive to anet flux therein for producing an output indicative of theferro-magnetic object proceeding along the right of way and through themagnetic field; and g. output logic means connected to said secondarycoil for detecting the signal change from the secondary coil as theferro-magnetic object proceeding along the right of way interrupts anddistorts the magnetic field generated from said primary coil.
 6. Theapparatus of claim 5 further including an additional secondary core withan additional secondary coil wound thereon and aligned adjacent to theprimary core similarly as the first secondary core in the magnetic fieldgenerated from the primary coil across a portion of the right of way, asecond device located within said additional secondary coil biased forcarrying a direct current responsive to a net flux for providing anobject presence signal; and said output logic means is connected to bothsecondary coils and is responsive to signal outputs of both devices forproviding directional indication relative to movement of theferro-magnetic object past the primary along the right of way.
 7. Theapparatus of claim 5 wherein said device is responsive for producing onepolarity signal or another in accordance with the direction of said netflux.
 8. The apparatus of claim 7 wherein said output logic means isresponsive to the signal output of said device for producing directionalindication of the movement of the ferro-magnetic object along the rightof way through the magnetic field in accordance with the polarity ofsaid device output.
 9. The apparatus of claim 5 wherein said devicecomprises a Hall-Effect solid state semi-conductor.